1. Field of the Invention
The present invention relates to a blue fluorescent compound and an organic electroluminescent device (OELD) and more particularly to a blue fluorescent compound having high color purity and high luminescent efficiency and an OELD using the red phosphorescent compound.
2. Discussion of the Related Art
Recently, a requirement for a flat panel display device having a relatively large display area and a relatively small occupancy has been increased. Among the flat panel display devices, an OELD has various advantages as compared to an inorganic electroluminescent device, a liquid crystal display device, a plasma display panel, and so on. The OELD device has excellent characteristics of a view angel, a contrast ratio and so on. Also, since the OELD device does not require a backlight assembly, the OELD device has low weight and low power consumption. Moreover, the OELD device has advantages of a high response rate, a low production cost and so on.
In general, the OELD emits light by injecting electrons from a cathode and holes from an anode into an emission compound layer, combining the electrons with the holes, generating an exciton, and transforming the exciton from an excited state to a ground state. A flexible substrate, for example, a plastic substrate, can be used as a base substrate where elements are formed. The OELD has excellent characteristics of a view angel, a contrast ratio and so on. Also, since the OELD does not require a backlight assembly, the OELD has low weight and low power consumption. Moreover, the OELD has advantages of a high response rate, a low production cost, a high color purity and so on. The OELD can be operated at a voltage (e.g., 10V or below) lower than a voltage required to operate other display devices. In addition, the OELD is adequate to produce full-color images.
A general method for fabricating OELDs will be briefly explained below. First, an anode is formed on a substrate by depositing a transparent conductive compound, for example, indium-tin-oxide (ITO). Next, a hole injection layer (HIL) is formed on the anode. For example, the HIL may be formed of copper phthalocyanine (CuPC), which is represented by following Formula 1-1, and have a thickness of about 10 nm to about 30 nm. Next, a hole transporting layer (HTL) is formed on the HIL. For example, the HTL may be formed of 4,4′-bis[N-(1-naphtyl)-N-phenylamino]-biphenyl (NPB) and have a thickness of about 30 nm to about 60 nm. Next, an emitting compound layer (EML) is formed on the HTL. A dopant may be doped onto the EML. For example, DPVBi, which is represented by following Formula 1-2, is used for the host, and BD-a, which is represented by following Formula 1-3, is used for the dopant. The EML includes the host and the dopant by about 1 to 10 weight % and has a thickness of about 20 nm to about 40 nm.

Next, an electron transporting layer (ETL) and an electron injection layer (EIL) are stacked on the EML. For example, the ETL may be formed of tris(8-hydroxy-quinolate)aluminum (Alq3). A cathode is formed on the EIL, and a passivation layer is formed on the cathode.
Various compounds for the EML have been introduced. However, there are limitations in the related art EML compound. As shown in FIG. 1, since the blue color has pure color purity, it is very difficult to produce a dark blue color. Accordingly, there is a problem to display a full color image. In addition, the blue color has lower luminescent efficiency.